1. Field of the Invention
Embodiments of the invention relates to a device for determining the wear of a carbon ceramic brake disk. The device includes at least one coil for generating a magnetic field in the brake disk and for detecting an eddy current in the brake disk.
2. Discussion of Background Information
A “carbon ceramic brake disk” is a brake disk comprising a carbon ceramic, wherein the carbon ceramic comprises a ceramic matrix as well as carbon fibers embedded in the matrix.
In such carbon ceramic brake disks an oxidation of the carbon fibers and therefore wear occurs due to high operating temperatures. This wear cannot be reliably recognized by mere optical inspection. An improved recognition of wear is achieved by inductive methods of measurement. The principle used in this type of measurements is based on eddy current damping; either using two coils (EP 1 387 166) operating continuously, or one or two coils in pulsed operation (DE 10 2008 051 802). The disclosures of EP 1 387 166 and DE 10 2008 051 802 are expressly incorporated by reference herein in their entireties. In these documents the excellent correlation between the inductive measurement and a gravimetric determination of the wear is disclosed. A conventionally traded profometer (www.proceq.com) is used as measuring device. Using these types of techniques, it is not necessary to disassemble the brake disk for measurement. It is also noted that the measuring values are independent on soiling and the presence of liquids.
The by far largest problem of such procedures lies in the fact that, due to the unavoidable inhomogeneity of the material, the measured values can differ strongly as a function of location (variations up to 100% are observed). A further variation is caused by the venting ducts extending within the disk. A conventional device can, upon a dislocation of a few millimeters, display a value that deviates by more than 10%. Since the drop of the measured value between a new and a worn disk is at approximately 40 to 50%, such a location dependence is greatly disadvantageous for a measurement.
DE 10 2008 051 802 describes a positioning technique by a gauge and mechanical positioning device, which, however, is found to non-viable.
Further it must be noted that reliable measuring values can only be recorded when the measuring device lies exactly against the disk, which leads to additional requirements regarding the shape of the device if the same is to be operated by hand at a location of service.
A further disturbing factor is due to the metallic elements, such as the caliper, axle shaft and fender, present around a built-in brake disk.